A thiocyanate stabilizing bath containing cyclohexanone bisulfite

ABSTRACT

Complexing bath for stabilizing silver image in silver halide emulsion which is not adequately fixed, is improved by addition of cyclic ketone bisulfite.

[52] US. Cl

United States Patent- AFGA-Gevaert Aktiengesellschait Leverkusen, Germany [73] Assignee [32] Priority Mar. 25, 1967 Germany A 55 261 [54] A Tl-llOCYANATE STABILIZING BATH CONTAINING CYCLOHEXANONE BISULFITE 1 Claim, No Drawings [51] Int.Cl G03c 5/38 [50] Field of Search 96/61 [56] References Cited UNITED STATES PATENTS 3,080,230 3/1963 Haydn et al 96/95 FOREIGN PATENTS 1,258,356 3/1961 France 96/61 277,975 8/1963 Australia 96/95 Primary Examiner-Norman G. Torchin Assistant Examiner-Mary F. Kelley Attorney-Connolly and l-lutz ABSTRACT: Complexing bath for stabilizing silver image in silver halide emulsion which is not adequately fixed, is improved by addition ofcyclic ketone bisulfitev A THIOCYANATE STABILIZING BATH CONTAINING CYCLOHEXANONE BISULFITE ln rapid reproduction processes, one may stabilize the developed photographic prints with complex-forming agents instead of by the classical method of fixing with sodium thiosulfate solution followed by washing with water. This stabilization process differs from the process of fixing in that the silver salts remain in the unexposed and undeveloped parts of the layer in the form of light-insensitive reaction products of the stabilizing agent with the original silver halides. The stabilization of developed photographic materials by the method carried out at present is not entirely satisfactory. For example, nearly all substances that form complexes with silver halides attack metallic silver, and therefore the photographic image by, converting silver into a silver salt. This causes a bleaching or brown discoloration of the silver image, i.e., the silver image disappears from the photograph in the course of time, especially in a moist atmosphere. The developers and their oxidation products present in the layer, especially the oxidation products of hydroquinone, also impair the keeping properties of the image.

It is also known that more stable stabilized images can be obtained by the addition of sulfite or bisulfite compounds,

such as sodium sulfite or potassium metabisulfite, to the stabilizing bath which is normally an ammonium thiocyanate solution. The addition of these compounds, however, is not entirely satisfactory in view of the pungent odor arising and the formation of crystalline deposits in the processing apparatus and on the stabilized images. These disadvantages can be overcome by employing addition compounds with aldehydes or ketones, instead of or in addition to the usual sulfite or bisulfite compounds. The aldehyde bisulfites and methyl ketone bisulfites have the disadvantage that when used alone, they do not protect the silver image sufficiently against the action of moist heat and that they impart an unpleasant odor to the finished prints.

The object of the invention is to provide an improved photographic process for the production of photographic images, which process is characterized by stabilization of the developed silver image in a final processing step. A particular object is to improve the keeping properties of the stabilized photographic image during prolonged storage even under extreme climatic conditions.

We now have found that the keeping properties of stabilized silver images can be improved by adding to the stabilization bath a cyclic ketone bisulfite of the following formula:

SOQX wherein n is 46; and

X is a sodium or potassium atom.

The cycloalkyl rings of the above formula may be further substituted, for example, with short-chained alkyl such as methyl. Cyclohexanone bisulfites have proved to be especially suitable.

The compounds can be prepared in known manner by reacting the ketone with sodium pyrosulfite. Cyclohexanone bisulfite is prepared as follows:

260 ml. of cyclohexanone are added dropwise, with stirring, to a solution of 190 g. of sodium pyrosulfite in 880 ml. of water. The precipitated product is suction-filtered and washed with 80 percent alcohol. The excess cyclohexanone is removed by extraction with methylene chloride.

The usual light-sensitive photographic materials comprising at least one silver halide emulsion layer may be used when carrying out the process according to the invention. The lightsensitive silver halide emulsions may contain any silver halides such as silver chloride or silver bromide, if desired with a small amount of silver iodide. Emulsions which are based on silver chloride, are preferred.

The usual water-permeable binding agents especially proteins and preferably gelatin, may be used for the light-sensitive silver halide emulsion layer.

Development is carried out in the usual manner, using the known developer substances. According to a preferred embodiment of the invention, the developer is added to the photographic material and development is initiated by treatment with an activator solution which consists substantially of an alkaline bath.

The usual stabilizers may be used in the process according to the invention, especially thiocyanates and in particular ammonium thiocyanate. These stabilizer solutions contain about 15 to 35 g. of stabilizer per 100 cc. of solution. These baths otherwise contain the usual other additives such as alkali metal sulfites or metabisulfites, acetic acid or its salts, and organic compounds, especially heterocyclic compounds which contain mercapto groups, such as l-phenyl-S-mercaptotetrazole. Especially suitable are organic compounds which form sparingly soluble silver salts.

The cycloalkanone bisulfites used in the process according to the invention are added to the stabilizer baths, preferably in quantities of 0.1 to 200 g./liter.

The cycloalkanonebisulfite-containing bath of the invention is characterized by an excellent stability. A stabilizing bath containing, for example, cyclohexanone bisulfite remains fully effective even if used for weeks. Images stabilized with such baths show even after storage under tropical condition an excellent stability.

Contrary thereto, a stabilizing bath which contains acetone bisulfite instead of .cyclohexanone bisulfite is sufficiently effective only if freshly prepared. If used for some days, photographic silver images stabilized with that bath begin to fade and to discolor.

EXAMPLE A light-sensitive photographic material comprising a silver chloride gelatin emulsion layer which contains hydroquinone (25 g. of hydroquinone per kg. of emulsion) and which is applied onto a paper support is exposed to form an image and developed using the following activator solution:

60 g. of sodium hydroxide 50 g. ofsodium sulfite (anhydrous) 2 g. ofpotassium bromide made up to l liter with water.

The'developed material is then cut into two strips. Strip 1 is treated with the following stabilizer solution:

250 g. of ammonium thiocyanate g. of potassium metabisulfite 20 ml. of 60 percent aqueous acetic acid 1 g. of l-phenyl-5-mercaptotetrazole made up to 1 liter with water.

The second strip is treated with a stabilizer solution which has the above composition but in addition contains 50 g. of cyclohexanone bisulfite per liter.

Both samples are processed in a two-bath developer apparatus of the usual construction. The treatment time is about 1-5 seconds in the activator and about 2-15 seconds in the stabilizer solutions.

To test the stability of the silver image, the developed and stabilized image is placed while still moist, immediately after leaving the developer apparatus, in a watertight bag, for example, a paper bag backed with aluminum or polyethylene, and the bag, is sealed to make it airtight and impervious to moisture, and is stored in a drying cupboard at 50 C. for 24 hours. The silver image of the sample which had been stabilized with a stabilizer solution containing cyclohexanone bisulfite shows no change, but the comparison sample shows a brown discoloration and fading starting from the corners.

We claim:

1. In the process of stabilizing an exposed and developed image in a silver halide emulsion in which the emulsion is first exposed to form an image, developed in a first activator solution and then treated in an aqueous thiocyanate stabilizing bath the improvement according to which the stabilizing bath also contains cyclohexanone bisulfite dissolved in an amount between 0.1 to 200 g./liter.

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